G-protein coupled receptors (GPCR) are a family of cell surface proteins involved in mediating many of the biological actions of neurotransmitters in the brain. It has been estimated that there are approximately 865 GPCRs in the human genome, making them one of the largest gene families known. The brain is particularly rich in GPCRs, expressing over 90% of all known non-sensory receptors. Approximately one third of these GPCRs are termed orphan GPCRs (oGPCRs), with no known ligand or function. Understanding the functions of CNS oGPCRs may provide opportunities in the development of new drugs to better treat common mental disorders affecting millions of people in the US. Omeros has employed a unique two-pronged approach to discovering drugs targeting oGPCRs. First, in vivo gene knockout technology is employed to identify potential functions of these oGPCRs and enable the selection of the most interesting oGPCRs to pursue. Second, we are investigating a novel in vitro technology for high throughput screening of ligands including antagonists, reverse agonists, and agonists to GPCRs. There is no requirement for control agonists which makes this technology ideal for screening oGPCRs. We will validate a high throughput assay based on this technology. This phase I SBIR will confirm that the technology can be utilized as a high through- put assay using GPCRs with known peptidergic and aminergic ligands. These receptors will be screened using both an industry standard activity based screen (FLIPR) and this novel assay. A finding that the same compounds can be identified by both assays will serve to validate this new, totally general assay technology. Such validation will allow Omeros to harness this assay to identify active ligands to a variety of exciting oGPCRs that have the potential to serve as targets for important CNS based disorders. PUBLIC HEALTH RELEVANCE: Approximately one third of the G-protein coupled receptors (GPCRs) that mediate many of the biological actions of neurotransmitters in the brain have no known ligand or function and are termed orphan GPCRs (oGPCRs). The goal of these studies is to validate a novel technology to discover drugs against any GPCR including oGPCRs. This validation will enable the discovery of active compounds targeting this important class of molecules and could result in the development of a new generation of CNS drugs.